Manual machine-tool comprising a braking means

ABSTRACT

The invention is based on a hand power tool, in particular a disk-type sander, that comprises a motor ( 12 ) with a drive shaft ( 14 ) located in a housing, whereby the drive shaft ( 14 )—by way of its side furthest from the motor ( 12 )—is joined via an eccentric ( 18 ) with a sanding disk ( 16 ) that can walk around an annular, turnably supported means ( 20, 72 ) that is capable of being braked via braking means ( 22, 62 ). 
     It is proposed that the annular means ( 20, 72 ) are supported in the braking means ( 22, 62 ).

BACKGROUND OF THE INVENTION

The invention is based on a hand power tool according to the preamble ofclaim 1.

A hand power tool, in particular a motor-driven off-hand grinder, ismade known in DE 199 52 108 A1, that comprises a motor with a driveshaft located in a housing. The drive shaft—by way of its side furthestfrom the motor—is joined via an eccentric sleeve with a sanding disk.Formed on the sanding disk—which is supported on the eccentric sleevevia a first bearing eccentrically relative to the drive shaft—is a firstannular means that comprises a first, radially outwardly facing rollingface. A second annular means having a radially inwardly facing, secondrolling face corresponding with the first rolling face is turnablysupported on the eccentric sleeve via a second bearing coaxially inrelation to the center axis of the drive shaft of the motor.

The second means is enclosed—over part of its area—by an elastic bandthat forms a braking means. The second annular means are capable ofbeing fixed in position in torsion-resistant fashion via the brakingmeans for a forced drive or for a rotating drive of the sanding diskthat superposes an orbital motion. The first rolling face of the firstannular means can walk around the second rolling face of the secondannular means, which leads to a rotary motion of the sanding disk. Ifthe braking means are released, the second means can be rotated, and aforced drive is stopped.

ADVANTAGES OF THE INVENTION

The invention is based on a hand power tool, in particular a disk-typesander, that comprises a motor with a drive shaft located in a housing,whereby the drive shaft—by way of its side furthest from the motor—isjoined via an eccentric with a sanding disk that can walk around anannular, turnably supported means that is capable of being braked viabraking means.

It is proposed that the annular means are supported in the brakingmeans. Advantageously, components—in particular bearing components—andinstallation space can be spared, and a robust, cost-effective devicecan be obtained that is compact in design, in the axial direction inparticular. Moreover, an encapsulated design having inboard rubbingsurfaces can be realized, by way of which said rubbing surfaces can beprotected against contamination, in particular against sanding dust.

If, during operation, an operator lifts the hand power tool away from asurface of a material to be worked, the sanding disk can reach a highrate of rotational speed due to the friction prevailing in a sandingdisk bearing and the absence of friction between the sanding disk andthe material. If the annular means have a permanent, active connectionwith the sanding disk, the sanding disk can be advantageously preventedfrom racing by means of forced rubbing between the annular means and thebraking means. A separate component for reducing rotational speed, inparticular a rubber lip joined with the housing in torsion-resistantfashion, can be avoided. Additional rubbing on the sanding disk andadditional loading of the sanding disk resulting therefrom can beprevented.

If the annular means has teeth, around which the sanding disk can walkvia corresponding teeth, a secure, slip-free connection can beadvantageously obtained with high efficiency. The connection between theannular means and the sanding disk can also be designed as a frictionconnection or a connection having undefined teeth, however.

If the annular means is formed by a belt, a cost-effective standardcomponent can be used that has low weight. If the belt is made ofrubber, a high amount of friction can be obtained with only slightcontact force. The belt can also be formed out of other componentsand/or other materials that appear reasonable to one skilled in the art,such as plastic, aluminum, etc. If the annular means is formed by a gearmade of aluminum, frictional heat can be dissipated via the annularmeans in particularly advantageous fashion.

If the cross-section of the annular means is designed trapezoidal inshape, a large contact surface can be obtained between the braking meansand the annular means, with which the torque occurring between theannular means and the braking means can be advantageously transferred.Moreover, an advantageous means of guiding the annular means in thebraking means can be obtained.

It is feasible, in principle, that the annular means and the brakingmeans are used solely to prevent the sanding disk from racing.Particularly advantageously, however, torque acting between the annularmeans and the braking means can be adjusted via a switching device. Ifthe annular means is arrested in the braking means in torsion-resistantfashion, a forced drive can be obtained, and the sanding disk can walkaround the annular means. By means of the walking-around motion, anorbital motion of the sanding disk supported eccentrically relative tothe motor shaft can be combined with a rotary motion of the sandingdisk, and a motion of the sanding disk can be obtained with which a highlevel of abrasion on the material to be worked can be achieved. If theset torque is exceeded, a slipping of the annular means in the brakingmeans can be achieved, and an overloading of the motor—in particularwhen the sanding disk is obstructed—can be advantageously prevented. Ifthe braking means are open and the annular means are turnably supportedin the braking means, a free-running operation of the sanding disk canbe obtained, and a particularly fine working of a surface can beachieved.

If the braking means are loaded via at least one spring element, asteady-state application of the torque acting on the annular means canbe achieved, and, in fact, when the spring element acts in the closingdirection of the braking means, or a reliable opening of the brakingmeans can be achieved when the spring element acts in the openingdirection of the braking means. If the spring element acts in theclosing direction, wear between the annular means and the braking meanscan be compensated. If the spring element acts in the opening directionof the braking means, a reliable opening of the braking means andoperation with low material abrasion can always be ensured. The springelement can be formed by a separate component, e.g., by a tension-loadedor compression-loaded helical compression spring, etc., or it can bedesigned integral with the braking means, e.g., by forming the brakingmeans out of spring steel.

In a further embodiment of the invention, it is proposed that brakingaction is produced by means of a force acting on the braking means inthe axial direction, by way of which the annular means can be reliablyprevented from jamming in the braking means. Moreover, cost-effectivebraking means and annular means having simple cross-sectional geometriescan be achieved.

The braking means can be designed as a single component or having twocomponents. If the braking means are designed with at least twocomponents, a particularly simple assembly can be obtained, whereby thebraking means can be divided into various layers appearing reasonable toone skilled in the art.

It is further proposed that the braking means comprises at least twojaws capable of pivoting around a pivot axis. An even load applied bythe braking means to the annular means can be advantgeously achievedusing simple design means.

Particularly advantageously, the pivot axis is located on a sideopposite from the switching device. A large lever arm can be obtained,via which the annular means can be arrested in the braking means via aswitching device using a small amount of force, and the hand power toolcan be switched into the forced-drive mode with a small amount of force.The jaws can be integrally interconnected in the region of the pivotaxis, or they can be designed separate in the region of the pivot axis,e.g., in that they are held together via a joint shell integral with thehousing.

SUMMARY OF THE DRAWINGS

Further advantages result from the description of the drawinghereinbelow. The drawings, the description, and the claims containnumerous features in combination. One skilled in the art willadvantageously consider them individually as well and combine them intoreasonable further combinations.

FIG. 1 shows a partial sectional drawing through a disk-type sander,

FIG. 2 shows a sectional drawing along the line II—II in FIG. 1, and

FIG. 3 shows a section of an alternative braking means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a partial sectional drawing of a disk-type sander having anelectric motor 12—located in a housing 10—with a drive shaft 14. On theside furthest from the electric motor 12, the drive shaft 14 is joinedwith a sanding disk 16 via an eccentric 18. The sanding disk 16 isturnably supported in the eccentric 18 eccentrically relative to thedrive shaft 14 via a journal 38 and a sanding disk bearing 40, and it issecurely joined with the journal 38 via a screw 42.

On its side closest to the electric motor 12, the sanding disk 16comprises a sanding pad carrier 44 holding a sanding pad 66 with aflange 46 facing the electric motor 12 in the axial direction (FIG. 1).On its radially outwardly facing side, the flange 46 has teeth 26 thatmesh in corresponding, radially inwardly facing teeth 24 of an annularmeans 20, and said flange has a permanent, active connection with theannular means 20.

The annular means 20 formed by a rubber belt has a trapezoidalcross-section and is turnably supported in a recess 48—having atrapezoidal cross-section—of a basically annular braking means 22 (FIGS.1 and 2). The braking means 22—supported in the housing 10 intorsion-resistant fashion concentrically with the drive shaft 14—nearlycompletely surrounds the rubber belt 20 in its circumferentialdirection. The braking means 22 have a first unit facing away from thesanding disk 16, and a second unit facing the sanding disk 16, wherebyeach of the units is divided into two jaws 34, 36 designed semicircularin shape.

The jaws 34, 36 are supported in a joint shell 74 integral with thehousing 10 in a fashion that allows them to pivot around a pivot axis32. On the side opposite from the pivot axis 32, the jaws 34, 36 arejoined via a switching device 28 (FIG. 2).

On the side closest to the switching device 28, a first projection 50extending in the radial direction is integrally molded on jaw 36, and asecond projection 52 extending in the radial direction is integrallymolded on jaw 34 (FIG. 2). An external side of the first projection 50has an active connection with an eccentric 54 of the switching device28, while an external side of the second projection 52 bears against thehousing 10. A compression-loaded helical compression spring 30 bears,with its ends, against the opposing internal sides of projections 50, 52and loads the braking means 22 in its opening direction.

The eccentric 54 is joined via a screw 56 with a lever 58 of theswitching device 28 (FIG. 2). Torque acting between the rubber belt 20and the braking means 22 can be adjusted on the braking means 22 by anoperator via the lever 58 and the eccentric 54 of the switching device28.

If the disk-type sander is in its free-running mode, the helicalcompression spring 30 presses—via the projections 50, 52—the brakingmeans 22 so far apart that the rubber belt 20 is turnably supported inthe recess 48 in nearly frictionless fashion. Residual frictionremaining between the braking means 22 and the rubber belt 20 preventsan undesired racing of the sanding disk 16 when, during operation, saidsanding disk is lifted away from a surface to be worked.

If the operator actuates the lever 58, the braking means 22 are loadedvia the eccentric 54 against a spring force of the helical compressionspring 30, and, in fact, until the rubber belt 20 is held in the brakingmeans 22 in torsion-resistant fashion, which brings about a forceddrive. With forced drive, the eccentrically supported sanding disk 16,with its teeth 26, can walk around the teeth 24 of the rubber belt 20supported concentrically and in torsion-resistant fashion in the brakingmeans 22 at a constant rotational speed. In addition to the orbitalmotion of the sanding disk 16, said sanding disk also executes a rotarymotion by walking around the rubber belt 20.

FIG. 3 shows a braking device 62 as an alternative to FIGS. 1 and 2.Components that essentially remain the same are labelled with the samereference numerals. Moreover, the description of the exemplaryembodiment shown in FIGS. 1 and 2 can be referred to with regard forfeatures and functions that remain the same. The description below isbasically limited to the differences from the exemplary embodiment shownin FIGS. 1 and 2.

The braking means 62—divided in the axial direction into a first unitfacing away from the sanding disk and a second unit facing the sandingdisk—can be loaded via a switching device 28 in the axial direction toproduce braking action. Each of the units has a semicircular jaw 64,64′, each of which has a collar 68, 70 in the radially outer regionfacing the other unit, whereby a rubber ring 72 having an essentiallyrectangular cross-section is guided in the radial direction through thecollars 68, 70. A plurality of helical compression springs 60 isdistributed around the circumference in the axial direction between thecollars 68, 70, which said helical compression springs load the brakingmeans 62 in its opening direction. Jaw 64 is capable of being adjustedin the axial direction via an eccentric 54.

Jaws 64, 64′ could also be adjusted in the axial direction via otherdevices appearing reasonable to one skilled in the art, e.g., viathreads, etc. Instead of numerous helical compression springs 60, a wavedisk spring could be used as well, which wave disk spring could belocated between one of the two semicircular jaws 64, 64′ and the rubberring 72. The wave disk spring could compensate for tolerances and wearbetween the individual components.

Reference Numerals 10 Housing 12 Motor 14 Drive shaft 16 Sanding disk 18Eccentric 20 Means 22 Braking means 24 Teeth 26 Teeth 28 Switchingdevice 30 Spring element 32 Pivot axis 34 Jaw 36 Jaw 38 Journal 40Sanding disk bearing 42 Screw 44 Sanding pad carrier 46 Flange 48 Recess50 Projection 52 Projection 54 Eccentric 56 Screw 58 Lever 60 Springelement 62 Braking means 64 Jaw 66 Sanding pad 68 Collar 70 Collar 72Means 74 Joint shell

1. A hand power tool in the form of an eccentric disk grinder, comprising a motor (12) with a drive shaft (14) located in a housing (10), whereby the drive shaft (14) is joined via an eccentric (18) end with a sanding disk (16), the eccentric end (18) of the drive shaft (14) facing away from said motor (12), said sanding disk (16) being movable on rolling contact inside an annular means (20, 72), said annular means (20, 72) being rotatably supported in said housing (10), said annular means (20, 72) being further capable of being braked via braking means (22, 62) connected to said housing (10), whereby the annular means (20, 72) is rotatably supported in said housing (10) via the braking means (22, 62).
 2. The hand power tool according to claim 1, wherein the annular means (20, 72) has a permanent, active connection with the sanding disk (16).
 3. The hand power tool according to claim 1, wherein the annular means (20, 72) comprise teeth (24) around which the sanding disk (16) is moveable via corresponding teeth (26).
 4. The hand power tool according to claim 1, wherein the annular means (20, 72) is in the form of a belt.
 5. The hand power tool according to claim 1, wherein the cross-section of the annular means (20) is trapezoidal in shape.
 6. The hand power tool according to claim 1, wherein torque acting between the annular means (20, 72) and the braking means (22, 62) can be adjusted by means of a switching device (28).
 7. The hand power tool according to claim 1, wherein the braking means (22, 62) is tensioned via at least one spring element (30, 60).
 8. The hand power tool according to claim 1, wherein braking action is produced by a force acting on the braking means (62) in an axial direction of the braking means.
 9. The hand power tool according to claim 1, wherein the braking means (22, 62) has at least two components.
 10. The hand power tool according to claim 1, wherein the braking means (22, 62) comprise at least two jaws (34, 36) capable of being pivoted around a pivot axis (32).
 11. The hand power tool according to claim 6, wherein the pivot axis (32) is located opposite from the switching device (28). 